Disclosed herein, in various embodiments, are stable, high performing nanoparticle compositions suitable for printing, such as by inkjet printing. In particular, there is provided a conductive ink formulation comprising silver nanoparticles which has optimal performance, such as, reduced coffee ring effect, improved adhesion to substrates, and extended drying time in the print head.
The benefits of silver nanoparticle technology for printed electronics application have been recently discovered. For example, ink formulations comprising silver nanoparticles have demonstrated very good printed results. However, due to batch to batch variation of the silver nanoparticle powders, especially those prepared at large scale, irreproducibility of printed performance still continues to be a problem. The major variation is the silver content. In particular, for some batches having silver nanoparticles at 90 wt % silver content (which is the weight of silver over the total weight of silver and organic stabilizers), many black dots (aggregates of silver nanoparticles) appear in the printed lines. As such, there is a need to further develop a robust ink formulation that can be able to maintain batch to batch variation of silver nanoparticle powders.
Furthermore, current metal nanoparticle compositions when deposited on a substrate often result in conductive metal ink lines that are too wide, exhibit a low conductivity, and have a “coffee ring effect.” Coffee ring effect is referred to herein as when the particles in a given droplet end up along the circumference of the circle having a very thin center where the droplet was deposited on the substrate (i.e. a non-uniform deposition). In a cross-section of the droplet, a bimodal line profile (two peaks) in a surface profile measurement is observed. The deposition of a conductive metal line that exhibits a coffee ring effect and/or that are otherwise too wide may limit the inks use in certain applications. Thus, there is a further need to develop an ink formulation to reduce the coffee ring effect.
Finally, there is also a need for generally continuing improvement of previous ink formulations to provide better performance, including but not limited to, improved adhesion to substrates and/or extended drying time in printheads.